Embodiments of the invention relate generally to X-ray medical imaging, and more particularly to systems and methods to perform a spectral mammography (SM) such as 2D/3D dual-energy contrast-enhanced (CE), or digital breast tomosynthesis (DBT) guided biopsy exams.
Spectral mammography (SM) is an X-ray imaging modality used to scan breasts for screening, diagnosis and/or interventional examinations. The effectiveness of spectral mammography is affected by numerous factors, one of which is the two-dimensional (2D) rendering of images obtained using SM.
Alternative systems to SM are also known for breast imaging. For example, a digital breast tomosynthesis (DBT) or mammography-tomography (mammo-tomo) system is a dedicated mammography system that acquires several (e.g., tens of) angularly offset projection images and reconstructs three-dimensional (3D) image datasets.
To further assist in the detection and treatment of abnormalities in the breast, and in particular to enhance the ability of the SM and DBT systems to differentiate cancers in the breast from other abnormalities, contrast agents, such as iodine, can be injected into the patient that travel to the region of interest (ROI) within the breast. The contrast agents are taken up in the blood vessels surrounding a cancerous lesion in the ROI, thereby providing a contrasting image for a period of time with respect to the surrounding tissue, enhancing the ability to locate the lesion.
The use of a contrast agent can be coupled with images of the ROI taken using dual-energy imaging processes and technology. In dual-energy imaging, low-energy (LE) and high-energy (HE) images are taken of the ROI. In particular, CESM (2D) and CE-DBT (3D) imaging modalities are performed with dual-energy technology. For each view (single view in CESM, multiple views for CE-DBT), a pair of images is acquired: 1 low-energy (LE) image, and 1 high-energy (HE) image. In CE-DBT, one can acquire non-paired HE and LE images for each view and still be able to reconstruct HE volume, LE volume and recombined CE volumes for the ROI. For example, HE and LE view can be interleaved during the tomo scan (alternatively HE, LE, HE, LE, HE, LE, etc. . . . ) with a switch from HE to LE then to HE again etc., for each angulated position of the X-ray tube. This is particularly interesting when the tomo scan is performed with a continuous sweep of the X-ray tube, as opposed to the step & shoot approach where images are acquired when the X-ray tube is immobile, enabling the acquisition of HE/LE pairs of images for each specific angle that is considered. The LE and HE images are usually obtained at mean energies above and below the K-edge of the contrast agent. At X-ray energies just above the k-edge of the contrast agent, the absorption of X-rays is increased resulting in an increase of contrast from the iodine contrast agent in the HE image.
In dual-energy 3D or stereotactic procedures, LE and HE image acquisitions are performed, with at least two different positions of the X-ray source with respect to the detector. The images are then recombined to display material-specific information with regard to the internal structure of the tissue being imaged. In the case of 3D CESM, for example, after the injection of contrast medium, dual-energy images are acquired at 2 or more positions of the tube with respect to the detector. For each of these tube angulations, the low and high-energy images are recombined to produce an image of the contrast medium surface concentration at each pixel. The LE and HE images are then recombined to provide an iodine-equivalent or dual-energy (DE) image(s) (for a single view in CESM, and for multiple views for CE-DBT), which in CE-DBT, are used to reconstruct a 3D volume. This description corresponds to the step & shoot mode of acquisition in CE-DBT. Image recombination can be performed based on simulations of the X-ray image chain, which in one suitable exemplary manner is described in United States Patent Application Publication No. 2008/0167552, which is expressly incorporated by reference herein in its entirety, via calibrations on a reference phantom, or any other suitable 3D-reconstruction process, as is known. Additionally, in the continuous mode of acquisition where the X-ray tube moves continuously with interleaved HE and LE images being taken, the LE images are used to reconstruct a LE 3D volume, and the HE images are used to reconstruct a HE 3D volume, with both volumes being recombined in a suitable manner to provide an iodine 3D volume. One can as well implement an algorithm that combines 3D-reconstruction and HE/LE recombination in a single step.
While this process is utilized in both diagnostic and interventional procedures, in one example, a typical contrast-enhanced (CE) dual-energy (DE) stereotactic/3D breast tissue biopsy procedure has one or several of the following steps:                1) Positioning of the patient on the mammography system and breast compression along with injection of contrast agent either prior to or after positioning        2) Acquisition of one or several 0° scout images to check that the lesion is correctly placed in the imaging area to be accessed by the biopsy or treatment mechanism        3) Acquisition at tube angulation A        4) Acquisition at tube angulation B, with B≠A        5) Localization of the lesion on the images acquired at angulation A and B and computation of the (x,y,z) coordinates of the lesion        6) Injection of anesthetics and preparation of the biopsy device        7) Acquisition at tube angulations A and B to check that lesion has not moved (optional)        8) Skin incision and insertion of the biopsy needle        9) Acquisition at tube angulations A and B to check that the needle is correctly positioned (optional)        10) Firing of the biopsy device to take tissue samples        11) Acquisition (at angulation A or B or at 0°) to check correct sampling of tissue (optional)        12) Insertion of biopsy clip (optional)        13) Acquisition to check correct positioning of clip (optional)        
In the above method, the steps correspond to a stereo procedure. However, the biopsy can also be performed with the reconstructed 3D volume. Then, in that situation, at least one of the following modified steps of the prior method is employed:                2) Acquisition of one or several DBT images to check that the lesion is correctly placed in the imaging area to be accessed by the biopsy or treatment mechanism        3) Acquisitions at a series of n angles A1, A2, . . . , An         4) Reconstruction of the 3D volume (usually delivering a set of r images parallel to the detector plane)        5) Localization of the lesion on one image from the reconstructed 3D volume where the targeted lesion is the most visible (which gives the z coordinate of the targeted lesion, the z-coordinate being related to the image number (from 1 to r) in the reconstructed series of images) and reading of the (x,y) coordinates of the lesion in the reconstructed image where the targeted lesion is the most visible.In steps 7) and 9) one can apply the stereo approach as initially described using the paired angles, or modified steps 3) and 4) as described above using the series of n acquisitions. In step 11) one can also use any of the n angles as described in modified step 3) above.        
In the implementation or performance of this procedure, when it is desired to guide a biopsy with CESM or CE-DBT images, it is necessary to generate these DE images at each step of the interventional exam (e.g., scout view, stereo pair or DBT sweep to localize the biopsy target, repeat of stereo pair or DBT sweep to control the position of the interventional device such as a needle, etc.). The primary reason for this is that the dual-energy acquisitions enable the clinician to obtain both morphological and material-specific images for each of these steps.
However, acquiring dual-energy images for each step in the procedure presents certain drawbacks regarding the effects of the procedure on the patient. These include the fact that the number of dual energy acquisitions for each step leads to additional X-ray dose to the patient, which is undesirable. Further, the increased number of usages of the X-ray tube to obtain the required dual energy images consequently increases thermal load placed on the X-ray tube. This can translate to aborted exposures during the procedure, resulting in incomplete images and/or procedure, as well as a decreased life of the X-ray tube based on the increased usage.
In addition, the number of DE images required in the procedure extends the time required for the completion of the procedure that can have an overall length of more than 20 minutes, with the breast or other tissue being imaged being maintained under compression for the entire length of the procedure.
Accordingly, it is desirable to develop a procedure and system for performing diagnostic and interventional, e.g. guided biopsy, procedures that addresses the drawbacks of the currently existing procedures and systems.